[Windows] Text is not displayed if the font has Underline or Strikeout and GC.setAdvanced(true)

[Phillipus]

Windows 11
Java 21
Latest SWT from I-builds

This is moved from eclipse-gef/gef-classic#1023

If a Font is used to draw text in a GC that has either Underline or Strikeout the text is not rendered if GC.setAdvanced(true)

The Underline or Strikeout for a Font can be set using a FontDialog:

Run the Snippet:

import org.eclipse.swt.graphics.Font;
import org.eclipse.swt.graphics.FontData;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class FontTest {
    
    public static void main(String[] args) {
        Display display = new Display();
        Shell shell = new Shell(display);
        shell.setLayout(new FillLayout());
        shell.setSize(200, 150);
        
        // Rather than open a FontDialog we'll create the Font from an equivalent FontData string which has underline set
        String fontString = "1|Arial|10.125|0|WINDOWS|1|-27|0|0|0|400|0|1|0|0|3|2|1|34|Arial";
        FontData fd = new FontData(fontString);
        Font font = new Font(display, fd);

        shell.addPaintListener(e -> {
            GC gc = e.gc;
            gc.setFont(font);

            gc.drawText("Hello World", 10, 10);
            
            gc.setAdvanced(true); // Comment this out to render text
            gc.drawText("Hello World", 10, 50);
        });

        shell.open();
        
        while(!shell.isDisposed()) {
            if(!display.readAndDispatch()) {
                display.sleep();
            }
        }
    }
}

It should look like this:

But looks like this:

[HeikoKlare]

I took a quick look into this to get an impression if it may be easy to fix. What I found is that in GC.drawText() there is an evaluation whether GDI+ needs to be used:

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

Line 2863 in 2d4d435

boolean gdip = useGDIP(hdc, chars);

If I understand correctly, this check ensures that a text is only drawn with GDI+ if it contains characters that cannot be handled by GDI. This was done because there seem to have been some (chinese) characters that were not rendered (properly) with GDI+ 15 years ago: https://bugs.eclipse.org/bugs/show_bug.cgi?id=305815
This looks contradictory as I would expect text to always be rendered with GDI+ in case GDI+ (i.e., advanced mode) is enabled. When I just remove that check, such that everything is drawn with GDI+, the snippet works for me (and the snippet that was broken 15 years ago as well). So maybe we could just get rid of all the non-GDI+ fallback logic here.

I will create a draft PR to test what happens if we remove that.

[HeikoKlare]

Turns out that this issue is highly related to:

• [Win32] Missing fonts don't play nice with FontMetrics and Transform #2978

They are both about fonts that are not properly handled by GDI+ text rendering. In case of this issue, it's the underline property; in the other issue it's about a non-existent font.
Both fail to properly render text in this line:

eclipse.platform.swt/bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/GC.java

Line 2997 in 2d4d435

Gdip.Graphics_DrawDriverString(gdipGraphics, lpGlyphs, result.nGlyphs, data.gdipFont, brush, points, 0, 0);

When printing the result of that method call, it is 2, which means "Invalid parameter", see: https://learn.microsoft.com/en-us/windows/win32/api/gdiplustypes/ne-gdiplustypes-status

This way of drawing is based on a calculation of the individual symbols and their positions based on GDI (not GDI+) functionality, for which a properly fitting non-GDI+ font has to be used. For some reason, this calculation seems to fail in the reported situations.
When exchanging the mentioned line with the implementation as done in the drawTextGDIP method, the rendering works:

long format = Gdip.StringFormat_Clone(Gdip.StringFormat_GenericTypographic());
Gdip.Graphics_DrawString(gdipGraphics, buffer, buffer.length, data.gdipFont, pt, format, brush);

I do not think this code can be fully removed as proposed in #3100, as there is, e.g., some special handling for showing delimiters. But I am pretty sure this code can be significantly simplified. There is quite some duplication between drawTextGDIP and drawText (both use GDI+) with the only functional differences I see being related to drawing delimiters and a different calculation of character positions (which was motivated by bad placement of characters when using GDI+ back then (https://bugs.eclipse.org/bugs/show_bug.cgi?id=289244).